The present invention relates to clarithromycin (see Merck Index, 12th edition (1996), page 2404) of formula I, a well known and useful antibacterial agent: 
A compound of formula I may be prepared in anhydrous form by known methods which typically require recrystallization of the crude product using various organic solvents or mixtures thereof for purification. A purified compound of formula I may be obtained in anhydrous form, e.g. with a water content of lower than 2%, e.g. clarithromycin crystal form II.
It has now surprisingly been found that a compound of formula I in pure form may be obtained from an aqueous medium in anhydrous form and in the form of a hydrate.
Thus in one aspect the invention provides a process for the production of a compound of formula I which comprises the steps of
(i) producing a solution of compound of formula I in the form of a salt in a solvent,
(ii) adjusting the pH, and
(iii) isolating a compound of formula I,
characterised in that the solvent in step (i) is an aqueous solvent medium which is selected from water or a mixture of water and organic solvent.
Advantages of the process include:
(i) elimination of large amounts of organic solvents according to the present invention in comparison with prior art processes, and
(ii) reducing the content of organic solvent in a compound of formula I, and
(iii) the process according to the present invention may be carried out on technical sale.
A process according to the present invention may be carried out as follows:
A compound of formula I, e.g. in crude form, as obtained in a production process, in the form of a salt, e.g. a salt with an acid, e.g. an acid as described below, may be dissolved in an aqueous solvent medium, or a compound of formula I in free form may be dissolved by addition of an acid, e.g. an organic acid, for example formic acid or acetic acid, or an inorganic acid, for example a hydrochloric, hydrobromic, nitric or sulphuric acid, preferably hydrochloric acid or sulphuric acid, to form in situ a salt with the dimethylamino group in 3xe2x80x2position of the sugar radical attached to the ring system in position 5. An aqueous solvent medium includes water or a mixture of water with one or more organic solvents, for example water miscible and water immiscible organic solvents, such as alcohols, e.g. methanol, ethanol or isopropanol; ketones such as acetone or methyl isobutyl ketone; alkyl esters such as of formic or acetic acid, e.g. methyl acetate, ethyl acetate, isopropyl acetate and butyl acetate; aromatic hydrocarbons such as toluene or xylenes, ethers such as tetrahydrofuran or methyl t-butyl ether; chlorinated hydrocarbons such as methylene chloride and amides such as monoalkyl and dialkyl amides, e.g. N-methylformamide, dimethylacetamide and dimethylformamide, preferably water or a mixture of water with alcohols, ketones and aromatic hydrocarbons, e.g. water or water containing 0.5 to 20% v/v, such as 1 to 15% v/v, organic solvent. An aqueous medium may, beside water, comprise one or more individual organic solvents, e.g. as described above. Appropriate reaction conditions for the production of a compound of formula I in the form of a salt according to the present invention may include, e.g.
(i) a temperature range of about xe2x88x9215xc2x0 C. up to the reflux temperature of the solvent system present, such as from xe2x88x9210xc2x0 C. to 50xc2x0 C., e.g. from xe2x88x925xc2x0 C. to 40xc2x0 C.;
(ii) an appropriate pressure, e.g. atmospheric pressure, and a pressure which is above or below atmospheric pressure; and
(iii) appropriate dilution, e.g. a dilution range between 1 g and 500 g of a starting compound of the formula I per liter of aqueous medium.
A resulting solution of a compound of formula I in the form of a salt in an aqueous solvent medium may be filtered, e.g. after charcoal treatment, to remove impurities and the pH of a filtered solution obtained may be adjusted to an appropiate value, e.g. by addition of a base. Suitable bases include, for example, an inorganic base, such as, for example ammonia or an alkali, e.g. sodium, potassium; earth alkali, e.g. calcium, magnesium; and ammonium; hydroxide, carbonate, bicarbonate; and an organic base, such as an amine, e.g. an alkyl amine, or a mixture of individual bases, e.g. as described above. A base may be preferably a hydroxide, e.g. sodium or ammonia; preferably in aqueous solution. The term xe2x80x9cappropriate pHxe2x80x9d includes a pH range wherein the compound of formula I is present in solution or suspension in the form of a free base. An appropriate pH value includes, e.g. about 7.0 to 10.0, such as 7.5 to 9.5, for example 8.0 to 9.0. A compound of formula I may precipitate and may be isolated, e.g. by a method as conventional, e.g. by centrifugation or filtration, and dried, for example at a temperature of about 30 to 100xc2x0 C. to provide a compound of formula I in pure form, e.g. having a low organic solvent content.
A compound of formula I may be obtained in the form of a hydrate or in anhydrous form depending on the reaction conditions, drying conditions, and on the type and amount of solvent used:
(A) If in the production of a compound of formula I exclusively water is used as the aqueous medium, a compound of formula I in the form of a stable hydrate may be obtained having
(I) a water content of about 9 to 12%, such as about 9.5 to 11.5%, e.g. 10.0 to 11.0%, e.g. 10.7 to 10.8%, if the process temperature is a temperature higher than 24xc2x0 C., such as 25 to 50xc2x0 C., e.g. 30 to 40xc2x0 C. or
(II) a water content of 5.5 to 8%, e.g. 6 to 7%, if the process temperature is lower than 25xc2x0 C., such as 15 to 24xc2x0 C., e.g. 20 to 24xc2x0 C.
A compound of formula I in the form of a hydrate having a water content of 9 to 12% may be crystalline. The differential scanning calorimetry of a compound of formula I in the form of a hydrate having a water content of 9 to 12% may show at a heating rate of 10xc2x0 C./min an endotherm, i.e. loss of water, between room temperature and 90xc2x0 C.; an exothermic transition, i.e. related to a phase transition, at about 127 to 140xc2x0 C.; and an endothermic peak at 224.6xc2x0 C., i.e. because of melting of a compound of formula I in the form of a hydrate having a water content of 9 to 12%. Thermal gravimetric analysis at a heating rate of 5xc2x0 C./minute may show a 9.2% weight loss between room temperature and 85xc2x0 C. X-ray powder diffraction patterns of a compound of formula I in the form of a hydrate having a water content of 9 to 12% are given in Table 1 and more detailed in Table 2.
In Tables 1 and 2 xe2x80x9cdxe2x80x9d denotes the interplanar spacing; I/I0 denotes the relative intensity and A denotes Angstrom.
A compound of formula I in the form of a hydrate having a water content of 5.5 to 8% may be crystalline. X-ray powder diffraction patterns of a compound of formula I in the form of a hydrate having a water content of 5.5 to 8% are given in Table 3 and more detailed in Table 4.
In Tables 3 and 4 xe2x80x9cdxe2x80x9d denotes the interplanar spacing; I/I0 denotes the relative intensity and A denotes Angstrom.
Thus in another aspect the present invention provides a compound of formula I in the form of a hydrate having a water content of 9 to 12%, for example in crystalline form, e.g. having a X-ray powder diffraction pattern of Table 1, or e.g. Table 2.
In another aspect the present invention provides a compound of formula I in the form of a hydrate having a water content of 5.5 to 8.0%, for example in crystalline form, e.g. having a X-ray powder diffraction pattern of Table 3, or e.g. Table 4.
(B) If in the production of a compound of formula I a mixture of water and an alcohol, e.g. methanol, ethanol or isopropanol, in a ratio of 6:1 to 15:1, such as e.g. 8:1 to 10:1, e.g. 9:1 is used as the aqueous medium, a compound of formula I in the form of a stable hydrate may be obtained having a water content of 5.5 to 8%, such as about 5.5 to 7.5%, e.g. 6 to 7%. An isolated compound of formula I may be dried
(I) at a temperature below 70xc2x0 C. to obtain a compound of formula I in the form of a hydrate having a water content below 5.5 to 8%, but may recover within several hours under normal environmental conditions to a water content of 5.5 to 8%, or
(II) at a temperature higher than 70xc2x0 C., e.g. at 110xc2x0 C. for several hours, e.g. 20 or more hours, to obtain a compound of formula I in anhydrous form, e.g. having a water content below 2%, which may be considered as an isomorphic desolvate of the hydrated product.
The differential scanning calorimetry of an isolated compound of the formula I having a water content of 5.5 to 8% may show at a heating rate of 10xc2x0 C./minute an endotherm, i.e. loss of water, between room temperature and 90xc2x0 C., an exothermic transition between about 140 to 175xc2x0 C., and an endothermic peak at 222.9xc2x0 C., i.e. the melting of the product. A compound of formula I in the form of a hydrate having a water content of 5 to 8% as well as a compound of formula I in anhydrous form may be crystalline, e.g. having a X-ray powder diffraction patterns of Table 5 and more detailed of Table 6.
In Tables 5 and 6 xe2x80x9cdxe2x80x9d denotes the interplanar spacing; I/I0 denotes the relative Intensity and A denotes Angstrom.
In another aspect the present invention provides a compound of formula I in the form of a hydrate having a water content of 5.5 to 8.0%, for example in crystalline form, e.g. having a X-ray powder diffraction pattern of Table 5, or e.g. Table 6.
Known anhydrous 6-O-methyl erythromycin A, e.g. currently on the market, shows a X-ray powder diffraction pattern as described in Table 7 below (crystalline form II of clarithromycin).
In yet another aspect the present invention provides a compound of formula I in anhydrous form, e.g. having a water content below 2%, for example in crystalline form, having a X-ray powder diffraction pattern of Table 5, or e.g. Table 6.
(C) If in the production of a compound of formula I a mixture of water containing very small amounts of a ketone, e.g. acetone is used as the aqueous medium
(I) in a v/v ratio water:ketone of, e.g. about 25:1, a compound of formula I in anhydrous form e.g. having a water content of less than 2%, may be obtained, for example in crystalline form, e.g. having a X-ray powder diffraction pattern of Table 5. An isolated compound of formula I in anhydrous form may be dried at a temperature below 70xc2x0 C. to obtain a pure compound of formula I in anhydrous form having a X-ray powder diffraction pattern of Table 5;
(II) in a v/v ratio water:ketone of, e.g. about 125:2, a mixture of a compound of formula I in the form of a hydrate having a X-ray powder diffraction pattern of Table 1 and a compound of formula I in anhydrous form having a X-ray powder diffraction pattern of Table 7 may be obtained. Upon drying of this mixture at a temperature above 70xc2x0 C. a pure compound of formula I in anhydrous form having a X-ray powder diffraction pattern of Table 7 (crystalline form II of clarithromycin) may be obtained.
In Table 7 xe2x80x9cdxe2x80x9d denotes the interplanar spacing; I/I0 denotes the relative intensity and A denotes Angstrom.
(D) If in the production of a compound of formula I a mixture of water containing very small amounts of an organic solvent, e.g. ethylacetate or toluene, is used as the aqueous medium in a v/v ratio water:organic solvent of, e.g. about 25:1, or less, for example, e.g. about 125:2, a compound of formula I in anhydrous form e.g. having a water content of less than 2%, may be obtained, for example in crystalline form, e.g. having a X-ray powder diffraction pattern of Table 7. An isolated compound of formula I in anhydrous form may be dried at a temperature below 70xc2x0 C. to obtain a pure compound of formula I in anhydrous form having a X-ray powder diffraction pattern of Table 7 (crystalline form II of clarithromycin).
(E) In the production of a compound of formula I In the form of a stable hydrate, e.g. obtained under the process conditions described under (A), a compound of formula I in anhydrous form, e.g. having a water content lower than 2.0% may be obtained after drying for several hours at temperatures higher than 70xc2x0 C., such as higher than 90xc2x0 C., e.g. at about 100 to 110xc2x0 C. A compound of formula I in anhydrous form, e.g. having a water content lower than 2.0% may be stable, non-hygroscopic and crystalline, e.g. having a X-ray powder diffraction pattern of Table 5, and may show similar characteristics to known anhydrous clarithromycins (crystalline form II of clarithromycin). Appropriate drying conditions may include an appropriate pressure, e.g. atmospheric pressure, and a pressure which is below atmospheric pressure, e.g. under vacuum.
A ciarithromycin in each of the novel forms according to the present invention, e.g. a compound of formula I, in the form of a hydrate, e.g. having a X-ray powder diffraction pattern described in any of Tables 1 to 6, and a compound of formula I in anhydrous form having a X-ray powder diffraction pattern described in Tables 5 or 6 shows similar activity characteristics to the known form of clarithromycin currently on the market. Clarithromycin in the form of a novel hydrate or in novel anhydrous form of the present invention may thus be used in the same indications and in the same dosages as known clarithromycin forms, e.g. forms currently on the market.
In another aspect the present invention provides a pharmaceutical composition comprising a therapeutically effective amount of a compound of formula I in the form of a stable hydrate, e.g. having a water content of approximately 5.5 to 12%, or in anhydrous form, having a X-ray powder diffraction pattern of Table 5, in combination with a pharmaceutically acceptable carrier.
In yet a another aspect the present invention provides a method of treating bacterial infections in a host mammal in need of such treatment comprising administering to the mammal a therapeutically effective amount of a compound of formula I in the form of a hydrate or in anhydrous form, preferably in combination with a pharmaceutically acceptable carrier.
The following examples may illustrate the invention without limiting its scope. All temperatures are given in degree Celsius and are uncorrected.